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Abstract:

An electrode material of the present invention includes a plurality of
particles capable of absorbing and desorbing lithium, and a plurality of
nanowires capable of absorbing and desorbing lithium. The particles and
the nanowires include silicon atoms. The plurality of nanowires are
entangled with each other to form a network, and the network is in
contact with at least two of the plurality of particles.

Claims:

1. An electrode material for an electrochemical device, said electrode
material comprising:a plurality of particles capable of absorbing and
desorbing lithium, and a plurality of nanowires capable of absorbing and
desorbing lithium,wherein said particles and said nanowires include
silicon atoms,said plurality of nanowires are entangled with each other
to form a network, andsaid network is in contact with at least two of
said plurality of particles.

2. The electrode material for an electrochemical device in accordance with
claim 1, wherein said particles and said nanowires further include at
least one element selected from the group consisting of oxygen, carbon,
and nitrogen.

3. The electrode material for an electrochemical device in accordance with
claim 1, wherein at least one of said particles and said nanowires
further include a metal element other than said silicon atoms.

4. An electrode for an electrochemical device, the electrode comprising
the electrode material in accordance with claim 1 and a carrier for
carrying said electrode material.

5. The electrode for an electrochemical device in accordance with claim 4,
wherein said carrier includes at least one material selected from the
group consisting of copper, nickel, and stainless steel.

6. An electrochemical device comprising the electrode in accordance with
claim 4, a counter electrode, and an electrolyte.

7. The electrochemical device in accordance with claim 6, wherein the
electrochemical device is a non-aqueous electrolyte secondary battery or
an electric double layer capacitor.

8. A method for producing the electrode material for an electrochemical
device in accordance with claim 1, the method comprising:(a) generating a
thermal plasma in an atmosphere including an inert gas;(b) placing a raw
material including silicon in said thermal plasma; and(c) depositing a
product obtained by allowing said raw material to pass through said
thermal plasma on a predetermined carrier.

Description:

FIELD OF THE INVENTION

[0001]The present invention relates mainly to an electrode material for
electrochemical devices and a method for producing the electrode
material. To be specific, the present invention relates to an improvement
of an electrode material for electrochemical devices.

BACKGROUND OF THE INVENTION

[0002]Nowadays, electronic devices such as personal computers and cell
phones are rapidly becoming portable, and for a power source for driving
such devices, a small and lightweight but high capacity electrochemical
device has been demanded.

[0003]For a material that achieves such an electrochemical device,
silicon, which is capable of absorbing and desorbing lithium ions, has
been gaining attention. For example, silicon has been gaining attention
as a negative electrode active material for achieving a high capacity
non-aqueous electrolyte secondary battery. This is because the
theoretical discharge capacity of silicon is about 4199 mAh/g, and this
is more than ten times the theoretical capacity of carbon materials,
which are widely used as a negative electrode active material currently.
Silicon can also be used as a negative electrode material for lithium ion
electric double layer capacitors, utilizing its lithium ion absorbing and
desorbing characteristics.

[0004]Also becoming increasingly important is development of
electrochemical devices such as varistors, in which ceramics and
semiconductors such as silicon are layered and which is used for
stabilizing voltage and protecting circuits in electronic devices.

[0005]However, when silicon is used as for example an alloy-type negative
electrode material for non-aqueous electrolyte secondary batteries,
silicon undergoes significant expansion and contraction when absorbing
and desorbing lithium ions. For example, the silicon volume expands to
approximately four times the original volume by absorbing lithium ions.
Thus, negative electrode active material particles crack, or the active
material layer is peeled off from the current collector, declining the
electron conductivity between the active material and the current
collector. As a result, battery performance such as cycle performance
declines.

[0006]Thus, there has been an attempt to decrease the volume change due to
the lithium ion absorption and desorption, by using an oxide, nitride, or
oxynitride of silicon or tin as the negative electrode active material,
despite a slight decline in discharge capacity.

[0007]Also, there has been an attempt to provide a space in the active
material layer in advance to absorb the volume expansion when lithium
ions are taken in.

[0008]For example, Japanese Laid-Open Patent Publication No. 2003-303586
(document 1) discloses a secondary battery electrode formed by depositing
a thin film comprising an active material on the current collector. To be
specific, in document 1, the columnar projection portions of a
predetermined pattern are formed on a thin film of active material. With
the gaps between the columnar projection portions, the volume expansion
of the active material is absorbed. Thus, the active material expansion
and contraction do not give a large stress to the current collector, and
the damage of the active material can be avoided. Document 1 describes
that the columnar projection portions are formed by the lift-off method.

[0009]Nanostructured anode material for lithium-ion batteries (G. X. Wang
and four others, International Meeting on Lithium Batteries 2006
abstracts, issued by Centre National de la Recherche Scientifique,
France, 2006, p. 325) (document 2) disclosed a use of a mixture made by
dispersing nano-sized silicon in aerosol containing carbon powder to make
a composite electrode plate for use as a negative electrode of a lithium
secondary battery. It further discloses a negative electrode for a
lithium secondary battery obtained by sublimating silicon powder, and
attaching silicon nanowire thinly on a stainless steel. Document 2
reports that the use of silicon nanowires achieves obtaining a capacity
of 3000 mAh/g and excellent cycle performance. In the manufacturing
method disclosed in document 2, only silicon nanowires are formed.

[0010]Silicon nanowires can also be made as in below.

[0011]For example, Japanese Laid-Open Patent Publication No. Hei 10-326888
(document 3) discloses a method in which nano-sized molten alloy drops
are formed on a substrate as a catalyst, and SiH4 is supplied to
allow silicon nanowires to grow below each molten alloy drop. In this
producing method as well, only silicon nanowires are formed on the
substrate.

[0012]Japanese Laid-Open Patent Publication No. 2005-112701 (document 4)
discloses a method in which silicon powder is sintered in a furnace of
1200° C. to obtain a sintered body, and this sintered body is
evaporated in an inert gas flow to allow silicon nanowires to grow on a
substrate disposed at a position where a temperature gradient of
10° C./cm or more is present within a temperature range between
1200° C. to 900° C. In this producing method as well, only
silicon nanowires are produced.

[0013]As disclosed in document 1, providing gaps in the active material
layer is effective for absorbing the active material volume expansion
when lithium ions are taken in. However, when the active material layer
has a plurality of scattered columnar projection portions and the cross
section of the columnar projection portion is large, the active material
particles themselves are vulnerable to damage by the expansion. On the
other hand, when the cross section of the columnar projection portion is
small, adhesiveness at the interface between the current collector and
the active material declines, easily causing the removal of the active
material from the current collector.

[0014]Silicon in nanowire form is more promising compared with those
highly rigid columnar particles in that silicon in nanowire form is
flexible. However, characteristics of silicon nanowires are yet to be
understood sufficiently. Further, there are rooms for improvement in
terms of characteristics necessary for developing silicon nanowires for
usage in devices.

[0015]For example, in the case of the electrode plate containing only
silicon nanowires as the negative electrode active material, as disclosed
in document 2, with only the nanowires, the adhesiveness between the
current collector and the active material is low. Thus, when the active
material expansion and contraction are caused by charge and discharge,
the active material is easily removed from the current collector,
declining cycle performance. Further, due to the large surface area of
silicon nanowires, silicon nanowires are partially oxidized to become
silicon oxide. Silicon oxide has a large irreversible capacity, which
declines battery capacity.

[0016]In the case of the manufacturing method of nanowires as disclosed in
document 3, since the silicon nanowires are formed below the catalyst, a
catalyst of molten metal such as Au and Al has to be formed on the
substrate with a predetermined pattern. Further, as a raw material for
nanowires, expensive and dangerous gas such as silane is necessary.

[0017]In the case of the manufacturing method of nanowires disclosed in
document 4, a step for attaching nanowires to the substrate becomes
necessary.

[0018]The present invention aims to solve the problems in developing
silicon nanowires for use in devices such as those mentioned in the
above, for example, the problem caused by the expansion of the electrode
material in electrochemical devices, and the problem of an increase in
irreversible capacity. To be specific, the present invention aims to
provide an electrode for an electrochemical device with a high battery
capacity or capacitance, and provide a simple manufacturing method
thereof.

BRIEF SUMMARY OF THE INVENTION

[0019]An electrode material for electrochemical devices of the present
invention includes a plurality of particles capable of absorbing and
desorbing lithium, and a plurality of nanowires capable of absorbing and
desorbing lithium. The particles and the nanowires contain silicon atoms.
The plurality of nanowires are entangled with each other to form a
network, and the network is in contact with at least two of the plurality
of particles.

[0020]In a preferred embodiment of the present invention, the particles
and the nanowires further contain at least one element selected from the
group consisting of oxygen, carbon, and nitrogen atoms.

[0021]In another preferred embodiment of the present invention, at least
one of the particles and the nanowires further contain a metal element
other than the silicon.

[0022]The present invention also relates to an electrode for
electrochemical devices. The electrode contains the electrode material
and a carrier for carrying the electrode material. The carrier preferably
includes at least one material selected from the group consisting of
copper, nickel, and stainless steel.

[0023]The present invention further relates to an electrochemical device
including the electrode, a counter electrode, and an electrolyte. The
electrochemical device is preferably a non-aqueous electrolyte secondary
battery or an electric double layer capacitor.

[0024]The present invention further relates to a method for producing the
electrode material. The method includes the steps of:

[0025](a) generating a thermal plasma in an atmosphere including an inert
gas;

[0026](b) placing a raw material containing silicon in the thermal plasma;
and

[0027](c) depositing a product obtained by allowing the raw material to
pass through the thermal plasma on a predetermined carrier.

[0028]While the novel features of the invention are set forth particularly
in the appended claims, the invention, both as to organization and
content, will be better understood and appreciated, along with other
objects and features thereof, from the following detailed description
taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0029]FIG. 1 is a schematic diagram illustrating an electrode material in
one embodiment of the present invention.

[0030]FIG. 2 is an electron micrograph illustrating an electrode material
in one embodiment of the present invention.

[0031]FIG. 3 is an electron micrograph illustrating nanowires entangled
with each other to form a network, contained in an electrode material in
one embodiment of the present invention.

[0032]FIG. 4 is a schematic diagram illustrating an example of a
manufacturing device for producing an electrode material of the present
invention.

[0033]FIG. 5 is a vertical cross section schematically illustrating a
coin-type test battery made in Examples.

DETAILED DESCRIPTION OF THE INVENTION

[0034]In the following, the present invention is described in detail with
reference to the FIGs.

[0035]An electrode material for electrochemical devices of the present
invention includes a plurality of particles capable of absorbing and
desorbing lithium ions, and a plurality of nanowires capable of absorbing
and desorbing lithium ions. The particles and nanowires include silicon
atoms. Further, the plurality of nanowires are entangled with each other
to form a network, and the network is in contact with at least two of the
plurality of particles.

[0036]FIG. 1 schematically illustrates an electrode material in one
embodiment of the present invention, and FIG. 2 illustrates an electron
micrograph of an electrode material in one embodiment of the present
invention. FIG. 3 illustrates an electron micrograph of an example of a
network of nanowires contained in an electrode material in one embodiment
of the present invention.

[0037]As shown in FIGS. 1 to 3, in an electrode material of the present
invention, a plurality of particles and a nanowire network are entangled
with each other. To be specific, as shown in the electron micrograph of
FIG. 3, a plurality of nanowires are entangled with each other to form a
nanowire network 22. The nanowire network 22 connects a particle 21a and
a particle 21b. That is, the nanowire network 22 is in contact with at
least two particles capable of absorbing and desorbing lithium ions,
i.e., the particles 21a and 21b.

[0038]The particle diameter of the particles is preferably 0.5 to 10
μm. Although the fiber diameter of the nanowires is not particularly
limited, it is preferably 10 nm to 500 nm, and further preferably 20 to
50 nm. The fiber length of the nanowires is not particularly limited and
may be selected as appropriate, as long as the network can be formed. For
example, the fiber length of the nanowires is preferably 0.1 to 10 μm.

[0039]The particle diameter of the particles, and the fiber diameter and
the fiber length of the nanowires can be determined by, for example,
observation with an electron microscope. The particle diameter of the
particles can be determined, for example, by determining the maximum
diameters of ten particles in the particles, and calculating the average
of the obtained maximum diameters. The fiber diameter and the fiber
length of the nanowires can also be determined in the same manner.

[0040]The weight ratio of the particles to the nanowires is preferably
85:15 to 45:55.

[0041]As described above, in the present invention, the nanowires
entangled with each other to form a network are in contact with at least
two particles. Since the particle diameter of the particles is small, the
particles can be brought into contact with the carrier with an
appropriate contact area. Thus, even when the particles expand, the
particles can be brought into close contact with the carrier. Further,
the nanowire network is entangled with the particles. Thus, the
separation of these materials from the carrier can be curbed.

[0042]That is, based on the present invention, even with the repetitive
expansion and contraction of the electrode material, a high capacity
electrode in which the separation of the electrode material from the
carrier is curbed can be provided. By using such an electrode,
reliability of the electrochemical device, for example, in terms of cycle
performance, can be improved.

[0043]The particles and the nanowires include silicon atoms. For example,
the particles and the nanowires may be composed only of silicon atoms.
Or, at least one of the particles and the nanowires may include silicon
atoms and an element other than silicon atoms. The element is preferably
at least one of, for example, oxygen, carbon, and nitrogen. The element
does not absorb or desorb lithium ions. Therefore, by including the
element in at least one of the particles and the nanowires, the volume
change of the particles and the nanowires at the time of charge and
discharge can be made small. The amount of the element may be
appropriately selected according to the volume change rate and the
battery capacity.

[0044]For example, the composition of the particles and the nanowire is
preferably SiOx (0≦x<2), SiNy (0<y<1), or
SiCz (0<z<1).

[0045]Or, at least one of the particles and the nanowires may include a
metal atom other than a silicon atom. By including a metal atom in the
particles and the nanowires, the electrical resistance between the
particles and the nanowires can be made small.

[0046]For the metal atom included in the particles and the nanowires,
copper, nickel, and iron may be mentioned. The amount of the metal atom
is selected appropriately based on the expansion rate and the discharge
capacity of the particles and the nanowires.

[0047]The electrode material may be used for an electrode for
electrochemical devices. The electrode for electrochemical devices may
include, for example, the electrode material and a conductive carrier
carrying the electrode material. For the material forming the carrier,
various metal materials such as copper, nickel, iron, and stainless
steel; and carbon materials may be used.

[0048]To be specific, the electrode material of the present invention may
be used, for example, as a negative electrode active material for
non-aqueous electrolyte secondary batteries. For the material forming the
conductive carrier (negative electrode current collector) carrying the
electrode material, for example, copper, nickel, and iron may be
mentioned.

[0049]The non-aqueous electrolyte secondary battery may include a negative
electrode containing the electrode material of the present invention, a
positive electrode, i.e., a counter electrode, and an electrolyte. The
positive electrode includes a positive electrode active material capable
of absorbing and desorbing lithium ions. For the positive electrode
active material, for example, LiCoO2, LiNiO2,
LiNi1/2Mn1/2O2, and LiNi0.5Co0.5O2 may be
used, but not limited to these materials.

[0050]The electrolyte includes a non-aqueous solvent and a solute
dissolved therein. For the non-aqueous solvent, for example, ethylene
carbonate, propylene carbonate, and ethyl methyl carbonate may be used.
These may be used singly, or may be used in combination of two or more.
For the solute, for example, LiCl and LiPF6 may be used. The
electrolyte for the non-aqueous electrolyte secondary battery is not
limited to the above-mentioned electrolytes.

[0051]The electrode material of the present invention may also be used as
a negative electrode material for a lithium ion electric double layer
capacitor. To be specific, the negative electrode for the capacitor may
be formed only of the electrode material of the present invention. Or,
the negative electrode may include the electrode material of the present
invention, and a conductive carrier carrying the electrode material. For
the conductive carrier, for example, a metal carrier may be used. The
material forming the metal carrier is preferably, for example, copper,
nickel, and iron.

[0052]The more the specific surface area of the electrode, the more the
capacitance. The electrode material of the present invention has a large
specific surface area, since it includes both of the particles capable of
absorbing and desorbing lithium ions and the nanowires capable of
absorbing and desorbing lithium ions. Therefore, by using the electrode
material of the present invention, the capacitance of the electric double
layer capacitor can be improved.

[0053]The electric double layer capacitor includes, for example, a
negative electrode including the electrode material of the present
invention, a positive electrode as the counter electrode, and an
electrolyte. For the positive electrode material included in the positive
electrode, a carbon material may be used. The electrolyte may include a
non-aqueous solvent and a solute dissolved therein. For the non-aqueous
solvent, for example, ethylene carbonate, propylene carbonate, and ethyl
methyl carbonate may be used. These may be used singly, or may be used in
combination of two or more. For the solute, LiCl and LiPF6 may be
used. The electrolyte for the electric double layer capacitor is not
limited to the above-mentioned electrolytes.

[0054]Further, the electrode material of the present invention may be used
as a material for varistors. For example, a varistor can be obtained by
forming a layer of the particles and the nanowires on a conductive
electrode, forming an oxide ceramic layer thereon, and further forming a
conductive electrode on the oxide ceramic layer. For the oxide ceramics,
for example, at least one selected from the group consisting of zinc
oxide, silicon carbide, and silicon nitride may be used.

[0055]An electrode material for electrochemical devices of the present
invention may be made, for example, by a method including the following
steps:

[0056](a) generating a thermal plasma in an atmosphere including an inert
gas;

[0057](b) placing a material containing silicon in the thermal plasma; and

[0058](c) depositing a product obtained by allowing the raw material to
pass through the thermal plasma on a predetermined carrier. The electrode
material of the present invention may also be made by a method other than
the producing method as mentioned above.

[0059]FIG. 4 shows an example of a manufacturing device used in the
manufacturing method.

[0060]The manufacturing device in FIG. 4 includes a reaction chamber 1. At
the upper portion of the reaction chamber 1, a torch 10 is disposed. In
the torch 10, electrodes (or coils) 2 are disposed. The torch 10
preferably has a cooling mechanism for cooling the electrodes (or coils)
2. For the cooling mechanism, for example, a water-cooling mechanism may
be used.

[0061]A supporting board 3 is disposed in the reaction chamber 1 directly
below the torch 10, and at the face of the supporting board 3 facing the
torch 10, a carrier 4 is disposed.

[0062]First, in the manufacturing device of FIG. 4, gas remained in the
reaction chamber 1 is removed by an air displacement pump 5. For the air
displacement pump 5, various vacuum pumps may be used. A vacuum pump
which can reduce pressure to a high vacuum is used preferably. By using
such a vacuum pump, the amount of impurities remained in the reaction
chamber 1 can be significantly reduced. Thus, the impurities can be
prevented from entering into the electrode material to be produced.

[0063]Afterwards, the reaction chamber 1 is filled with a gas for
generating a thermal plasma. That is, the reaction chamber 1 is filed
with an atmosphere including an inert gas.

[0064]In the manufacturing device, the thermal plasma is generated in the
torch 10. Herein, the thermal plasma refers to a plasma with high thermal
energy. The electrons, ions, and neutral particles included in the
thermal plasma all have a high and substantially the same temperature.
The temperature of the electrons, ions, and neutral particles is, at the
highest portion, for example, 10000 to 20000K. The thermal plasma can be
generated by allowing the pressure in the atmosphere including the inert
gas in the reaction chamber 1 to be a high pressure of about atmospheric
pressure.

[0065]The method for generating the thermal plasma is not particularly
limited. For example, a thermal plasma can be generated by supplying an
electric power to the electrode (or coil) 2 from a power source 9, and
supplying the inert gas in a cylinder 6 to the torch 10 via a valve 7.
For the inert gas, for example, argon gas, helium gas, neon gas, krypton
gas, and xenon gas may be used.

[0066]To be specific, a thermal plasma can be generated in the torch 10 by
using a pair of electrodes 2 by applying a direct current voltage between
the electrodes 2 facing each other. A thermal plasma can also be
generated in the torch 10 by using the coil 2 by applying a
high-frequency voltage to the coil 2. Among these, the method using a
high-frequency voltage is preferable. The coil to which a high-frequency
voltage is applied can be disposed at the perimeter of the torch 10,
which makes maintenance of the coil easy. Also, although there may be a
possibility that the material forming the electrode enters into the
electrode material as impurities in the case when a direct current
voltage is applied to a pair of electrodes, in the method using a
high-frequency voltage, plasma does not make a contact with the coil, and
therefore the impurities of the material forming the coil can be
prevented from being mixed therein. Further, since the raw material
containing silicon can be easily evaporated or decomposed, the fiber
diameter of the nanowires can be easily made nano-sized. In FIG. 4, the
coil 2 is disposed at the perimeter of the torch 10 for applying a
high-frequency voltage. In this case, the torch 10 can be made, for
example, cylindrical. The size such as the inner diameter of the torch 10
is not particularly limited.

[0067]The speed of the supply of the inert gas into the torch 10 is
preferably 5 to 500 L/min.

[0068]In the case when a high-frequency voltage is used, the frequency of
the high-frequency voltage is preferably 1 to 100 MHz. The output applied
to the coil is preferably 10 to 300 kW.

[0069]To generate a thermal plasma stably and efficiently, a diatomic
molecule gas that is different from the inert gas is preferably supplied
to the torch 10 with the inert gas. The diatomic molecule gas can be
introduced to the torch 10 from the cylinder 6a via the valve 7a. For the
diatomic molecule gas, hydrogen gas, nitrogen gas, and oxygen gas may be
mentioned.

[0070]To stabilize the plasma, the flow rate of the inert gas and the flow
rate of the diatomic molecule gas are preferably controlled by using a
mass flow controller.

[0071]The supply speed of the diatomic molecule gas to the torch 10 is
preferably 5 to 500 L/min.

[0072]The inert gas and the diatomic molecule gas are, for example,
preferably supplied from the torch 10 in a direction toward the
supporting board 3.

[0073]While the inert gas is being supplied to the torch 10, i.e., into
the reaction chamber 1, the gas inside the reaction chamber 1 can be
discharged outside with the air displacement pump 5, so as to make the
pressure in the reaction chamber constant.

[0074]The raw material including silicon is supplied to the thermal plasma
in the torch 10 by the raw material feeder 8. In the case of the thermal
plasma generated by applying a high-frequency voltage to the coil, for
example, the raw material may be supplied to the thermal plasma so as to
move along the central axis of the thermal plasma.

[0075]The raw material is dissolved, evaporated or decomposed in the
thermal plasma, while being allowed to move vertically downwardly from
the torch 10 toward the carrier 4. Since the temperature of the thermal
plasma decreases as the raw material moves from the torch 10 to the
carrier 4, particles including silicon atoms and nanowires including
silicon atoms are generated. These particles and nanowires are deposited
on the carrier 4. That is, on the carrier 4, a product generated by
allowing the raw material including silicon to pass through the thermal
plasma (particles including silicon atoms and nanowires including silicon
atoms) is deposited. The electrode material of the present invention can
be thus made.

[0076]There has been reported that nanowires are more likely to be
generated at a portion where a solid phase, a liquid phase, and a vapor
phase coexist. In the above manufacturing method, by placing a raw
material including silicon having a larger particle diameter than the
particles including the silicon atoms in the thermal plasma, a portion of
the raw material changes into liquid or gas, to generate a portion where
a solid phase, a liquid phase, and a vapor phase coexist, and generate
the particles including silicon atoms along with the nanowires.

[0077]The temperature near the carrier 4 is preferably for example 600 to
1500° C. The temperature near the carrier 4 can be controlled, for
example, by adjusting the energy of the thermal plasma and the distance
from the torch 10 to the supporting board 3. The temperature near the
carrier 4 can be measured, for example, by measuring the infrared
radiation emitted from near the carrier by using a radiation thermometer.
The temperature near the carrier 4 can also be measured by setting a type
R thermocouple with its surface covered by an insulating material with a
high melting point such as alumina, and measuring the voltage of the
thermocouple.

[0078]The raw material including silicon is preferably in powder form,
since it is a low-cost. The raw material powder can be supplied, for
example, by using a feeder using pressure gas, a feeder capable of belt
conveyance, and a parts feeder.

[0079]The feeding of the raw material powder may be carried out
continuously or intermittently.

[0080]For the raw material including silicon, for example, silicon powder
and silicon oxide (SiOx) may be used.

[0081]The raw material including silicon is preferably supplied to the
thermal plasma at a speed of 1 to 50 g/min.

[0082]The particle diameter of the particles, and the fiber diameter and
the fiber length of the nanowires can be controlled by adjusting the
manufacturing conditions.

[0083]For the material forming the reaction chamber 1, the torch 10, and
the supporting board 3, those materials known in the art may be used. For
example, for the reaction chamber 1, the material is not particularly
limited, as long as an inert gas atmosphere can be created therein. For
the material forming the torch 10, ceramics (quartz and silicon nitride)
may be used. For the materials forming the supporting board 3, for
example, stainless steel, titanium, nickel, and iron may be mentioned.

[0084]The materials forming the carrier 4 are not particularly limited. A
conductive material, a semiconductive material, or a nonconductive
material may be used. For the conductive material, various metal
materials such as copper, nickel, and stainless steel, and carbon
materials may be used. For the semiconductive material, silicon simple
substance and SiCz may be used. For the nonconductive material,
various metal oxides and metal nitrides may be used. For the material
forming the carrier 4, silicon oxide and silicon nitride may be used.

[0085]The electrode including the electrode material of the present
invention can be made by using a conductive carrier, and depositing the
particles including silicon atoms and nanowires including silicon atoms
thereon. In this case, the conductive carrier functions as the current
collector.

[0086]In the case when the particles including silicon atoms and the
nanowires including silicon atoms are deposited on the semiconductive
carrier or the nonconductive carrier, the layer including the particles
and the nanowires may be removed from the carrier, and the obtained layer
or powder including the particles and the nanowires may be used as the
electrode material.

[0087]The particles and the nanowires including silicon atoms and at least
one element selected from the group consisting of oxygen, nitrogen, and
carbon can be obtained by further supplying a gas of oxygen source, a gas
of nitrogen source, and/or a gas of carbon source to the torch 10. For
the gas of oxygen source, for example, oxygen gas may be mentioned. For
the gas of nitrogen source, for example, nitrogen gas may be mentioned.
For the gas of carbon source, for example, ethylene gas may be mentioned.

[0088]The particles and the nanowires including silicon atoms and an atom
of metal other than silicon atoms can be obtained by depositing an active
material layer including the silicon particles and the silicon nanowires
on the carrier including the metal atom, and heat-treating the carrier
carrying the active material layer. Or, the particles and the nanowires
including silicon atoms, and a metal atom other than the silicon atoms
can also be made by placing a raw material including silicon, and a raw
material including the metal atom in the torch 10.

EXAMPLES

[0089]In the following Examples, electrode materials were made by using
the manufacturing device as shown in FIG. 4. For the thermal plasma, a
high-frequency thermal plasma was used. The obtained electrode materials
were used as the electrode materials for a non-aqueous electrolyte
secondary battery. In Examples below, as shown in FIG. 5, a coin-type
test battery was made, and a metal lithium was used as a counter
electrode. As described above, an electrode including an electrode
material of the present invention functions as a negative electrode, in
the case of a non-aqueous electrolyte secondary battery using for example
a lithium-containing composite oxide as the positive electrode active
material.

Example 1

Electrode Material Preparation

[0090]A supporting board 3 was fixed at a position directly below and
about 300 mm from a torch 10. On the supporting board 3 in a reaction
chamber 1, a copper foil with a thickness of 75 μm was disposed as a
carrier 4. The copper foil functions as a current collector in the
battery.

[0091]Afterwards, the gas in the reaction chamber 1 was displaced by using
an air displacement pump 5, and then the reaction chamber 1 was charged
with an argon gas. Such operation was repeated several times, to render
the atmosphere in the reaction chamber 1 an argon gas atmosphere.

[0092]Then, while introducing an argon gas at a flow rate of 200 L/min
from a cylinder 6 and a hydrogen gas at a flow rate of 10 L/min from a
cylinder 6a to the torch 10, a high-frequency voltage of 3 MHz was
applied to the coil 2, to generate a thermal plasma. The output applied
to the coil was set to 100 kW. At this time, the air displacement pump 5
was used to discharge gas in the reaction chamber 1, so that the pressure
in the reaction chamber 1 was constant.

[0093]Silicon powder (raw material) with a particle diameter of about 10
μm was introduced into the torch 10 at a speed of 25 g/min by using a
raw material feeder 8 to form an active material layer on the copper
foil. The active material layer formation was carried out for 10 minutes.
An electrode 19 including a copper foil 13 and an active material layer
14 carried thereon was thus obtained. The thickness of the active
material layer 14 was about 10 μm.

[0094]As the obtained electrode was observed by an electron microscope, it
was found that silicon particles with a particle diameter of about 5
μm, and silicon nanowires entangled to form a network, such as those
shown in FIG. 1, were deposited on the copper foil. Two silicon particles
adjacent to each other were in contact with the network of silicon
nanowires. The fiber diameter of the produced nanowires was 0.03 to 0.05
μm (30 to 50 nm).

(Battery Assembly)

[0095]A coin-type test battery as shown in FIG. 5 was made as in below.
The steps below were carried out in a dry air with a dew point of
-50° C. or less.

[0096]First, a metal lithium foil 16 with a diameter of 17 mm and a
thickness of 0.3 mm was obtained. The obtained metal lithium foil 16 was
disposed at an inner bottom face of a stainless steel-made sealing body
18.

[0097]Then, on the metal lithium foil 16, a polyethylene-made separator 15
was stacked. Afterwards, the electrode 19 obtained as described above was
disposed on the separator 15, so that the active material layer 14 faced
the metal lithium foil 16 with the separator 15 interposed therebetween.
On the electrode 19, a disc spring 17 was disposed.

[0098]Then, an electrolyte was injected to fill the sealing body 18, and
the stainless steel-made case 11 was disposed on the disc spring 17. The
end portion of the case 11 was crimped to the sealing body 18 with a
stainless steel-made gasket 12 interposed therebetween, to seal the
battery. The electrolyte was prepared by dissolving LiPF6 in a
non-aqueous solvent including ethylene carbonate and ethyl methyl
carbonate at a volume ratio of 1:3 with a concentration of 1.25 mol/L.

[0099]A battery of Example 1 was thus made.

Example 2

[0100]An electrode was made in the same manner as Example 1, except that
to the torch 10, an oxygen gas was further introduced at a flow rate of 5
L/min. Observation of the thus obtained electrode with an electron
microscope revealed that particles with a particle diameter of about 5
μm, and nanowires entangled with each other to form a network were
generated. The fiber diameter of the produced nanowires was 0.03 to 0.05
μm. By using an X-ray micro analyzer, it was confirmed that the
particles and the nanowires included 1:0.2 molar ratio of silicon and
oxygen. To be specific, the composition of the particles and the
nanowires was SiO0.2.

[0101]By using the obtained electrode, a battery of Example 2 was made in
the same manner as Example 1.

Example 3

[0102]An electrode was made in the same manner as Example 1, except that
to the torch 10, a nitrogen gas was further introduced at a flow rate of
10 L/min. Observation of the thus obtained electrode with an electron
microscope revealed that particles with a particle diameter of about 5
μm and nanowires entangled with each other to form a network were
generated. The fiber diameter of the produced nanowires was 0.03 to 0.05
μm. By using an X-ray micro analyzer, it was confirmed that the
particles and the nanowires included 1:0.1 molar ratio of silicon and
nitrogen. To be specific, the composition of the particles and the
nanowires was SiN0.1.

[0103]By using the obtained electrode, a battery of Example 3 was made in
the same manner as Example 1.

Example 4

[0104]An electrode was made in the same manner as Example 1, except that
to the torch 10, an ethylene gas was further introduced at a flow rate of
10 L/min. Observation of the thus obtained electrode with an electron
microscope revealed that particles with a particle diameter of about 5
μm, and nanowires entangled to form a network were generated. The
fiber diameter of the produced nanowire was 0.03 to 0.05 μm. By using
an X-ray micro analyzer, it was confirmed that the particles and the
nanowires included 1:0.15 molar ratio of silicon and carbon. To be
specific, the composition of the particles and the nanowires was
SiC0.15.

[0105]By using the obtained electrode, a battery of Example 4 was made in
the same manner as Example 1.

Example 5

[0106]The electrode thus obtained in Example 1 was put into an atmosphere
furnace, and heat-treated in an argon gas atmosphere at 500° C. By
using an X-ray micro analyzer, it was confirmed that silicon particles
and silicon nanowires present near the copper foil included copper atoms
of about 1 wt %.

[0107]A battery of Example 4 was made in the same manner as Example 1,
using the electrode after the heat-treatment.

Comparative Example 1

[0108]The silicon particles with a particle diameter of about 5 μm,
graphite as a conductive agent, and styrene butadiene rubber as a binder
were mixed in a weight ratio of 70:23:7. The obtained mixture was dried
at 120° C. for 12 hours to obtain an electrode material mixture.

[0109]Battery of Comparative Example 1 was made in the same manner as
Example 1, except that the electrode material mixture made as described
above was used instead of the electrode 19 made in Example 1. In
Comparative Example 1, the thickness of the active material layer was 15
μm.

Comparative Example 2

[0110]Silicon particles with a particle diameter of about 5 μm was
placed in an alumina crucible, and the crucible was placed in an air
atmosphere furnace. The temperature of the air atmosphere furnace was
increased to 800° C., and the temperature was kept for about 3
hours, to obtain silicon oxide particles.

[0111]By using an X-ray micro analyzer, it was confirmed that the silicon
oxide particles included 1:0.2 molar ratio of silicon and oxygen. To be
specific, the composition of the silicon oxide particles was SiO0.2.

[0112]A battery of Comparative Example 2 was made in the same manner as
Comparative Example 1, except that silicon oxide particles were used
instead of the silicon particles.

Comparative Example 3

[0113]Silicon powder with a particle diameter of about 5 μm was placed
in an alumina crucible, and the crucible was placed in an atmosphere
furnace. Then, while a mixed gas of 80 volume % nitrogen gas and 20
volume % hydrogen gas was allowed to flow into the atmosphere furnace at
a flow rate of 3 NL/min, the temperature of the atmosphere furnace was
increased to 1200° C., and the temperature was kept for 5 hours.
The silicon nitride particles were thus obtained.

[0114]By using an X-ray micro analyzer, it was confirmed that the silicon
nitride particles included 1:0.1 molar ratio of silicon and nitride. To
be specific, the composition of the silicon nitride particles was
SiN0.1.

[0115]A battery of Comparative Example 3 was made in the same manner as
Comparative Example 1, except that the silicon nitride particles were
used instead of the silicon particles.

Comparative Example 4

[0116]Silicon powder with a particle diameter of about 5 μm was placed
in an alumina crucible, and the crucible was placed in an atmosphere
furnace. Then, while introducing a mixed gas of 50 volume % argon gas and
50 volume % ethylene gas into the atmosphere furnace at a flow rate of 3
NL/min, the temperature of the atmosphere furnace was increased to
1250° C., and the temperature was kept for 5 hours. The silicon
particles including carbon atoms were thus obtained.

[0117]By using an X-ray micro analyzer, it was confirmed that the silicon
particles including carbon atoms included 1:0.15 molar ratio of silicon
and carbon. To be specific, the composition of the silicon particles
including carbon atoms was SiC0.15.

[0118]A battery of Comparative Example 4 was made in the same manner as
Comparative Example 1, except that the silicon particles containing the
carbon atoms were used instead of the silicon particles.

[Evaluation]

[0119]The batteries of Examples 1 to 5 and Comparative Examples 1 to 4
were examined for their discharge performance. To be specific, constant
current charge and discharge were repeated with a current density of 100
fA/cm2 and within a range of 0 to 1.5 V (Li/Li.sup.+ base). The
current density is a current value per unit area of the electrode 19.

[0120]The discharge capacity of the first cycle (initial discharge
capacity) and the discharge capacity of the 5th cycle were measured. The
measurement temperature was 20° C. The results are shown in Table
1. In Table 1, the initial discharge capacity and the discharge capacity
of the 5th cycle were shown as a discharge capacity per unit weight of
the active material.

[0121]Comparisons were made between the battery of Example 1 and the
battery of Comparative Example 1. The battery of Example 1 had a higher
initial discharge capacity than the battery of Comparative Example 1, and
decline in the discharge capacity at the 5th cycle was kept low. The
battery of Example 1 included nanowires including silicon, other than the
particles including silicon. In the battery of Example 1 after the charge
and discharge cycle, it was confirmed that the silicon particles and the
silicon nanowires were in close contact without being removed from the
copper foil. Probably, with the further inclusion of the nanowires, even
with the expansion of the active material while being charged, the
removal of the active material from the current collector was further
curbed. Thus, the decline in the initial discharge capacity and the
discharge capacity at the 5th cycle was moderated.

[0122]Comparisons were made between the battery of Example 2 and the
battery of Comparative Example 2. The battery of Example 2 had a higher
initial discharge capacity than the battery of Comparative Example 2, and
the decline in the discharge capacity at the 5th cycle was kept low. The
battery of Example 2 included, other than the particles including silicon
atoms and oxygen atoms, the nanowires including silicon atoms and oxygen
atoms. In the battery of Example 2 after charge and discharge cycle, it
was confirmed that the particles and the nanowires were in close contact,
without being removed from the copper foil. Provably, in the case of
Example 2 as well, similarly to the case of Example 1, the removal of the
active material from the current collector was curbed, and the decline in
the initial discharge capacity and the discharge capacity at the 5th
cycle was moderated.

[0123]Comparisons were made between the battery of Example 3 and the
battery of Comparative Example 3. The battery of Example 3 had a higher
initial discharge capacity than the battery of Comparative Example 3, and
the decline in the discharge capacity at the 5th cycle was kept low. The
battery of Example 3 included, other than the particles including silicon
atoms and nitrogen atoms, the nanowires including silicon atoms and
nitrogen atoms. In the battery of Example 3 after the charge and
discharge cycle, it was confirmed that the particles and the nanowires
were in close contact without being removed from the copper foil. In
Example 3 as well, probably, the removal of the active material from the
current collector was curbed, and the decline in the initial discharge
capacity and the discharge capacity at the 5th cycle was moderated.

[0124]Comparisons were made between the battery of Example 4 and the
battery of Comparative Example 4. The battery of Example 4 had a higher
initial discharge capacity than the battery of Comparative Example 4, and
the decline in the discharge capacity at the 5th cycle was kept low. The
battery of Example 4 included, other than the particles including silicon
atoms and carbon atoms, the nanowires including silicon atoms and carbon
atoms. In the battery of Example 4 after the charge and discharge cycle,
it was confirmed that the particles and the nanowires were in close
contact without being removed from the copper foil. In Example 4 as well,
probably, the removal of the active material from the current collector
was curbed, and the decline in the initial discharge capacity and the
discharge capacity at the 5th cycle was moderated.

[0125]The battery of Example 5 had a lower initial discharge capacity than
the battery of Example 1, but the decline in the discharge capacity at
the 5th cycle was kept low. Probably, since the silicon particles and the
silicon nanowires included copper atoms, the initial discharge capacity
declined, but the electron conductivity of the silicon particles and the
silicon nanowires increased, and as a result, the capacity decline when
charge and discharge were repeated was kept low. In the battery of
Example 5 after the charge and discharge cycle as well, it was confirmed
that the particles and the nanowires were in close contact, without being
removed from the copper foil.

[0126]As described above, in the non-aqueous electrolyte secondary
batteries of Examples 1 to 5, the removal of the active material
including particles with silicon atoms and the nanowires with silicon
atoms from the current collector can be curbed. Therefore, an
electrochemical device including the electrode material of the present
invention has a high capacity and excellent cycle performance.

[0127]An electrochemical device including an electrode material of the
present invention may be used, for example, as a power source for driving
mobile electronic devices such as for example personal computers and
mobile phones. Further, the electrochemical device may also be used for
stabilizing voltage and protecting a circuit.

[0128]Although the present invention has been described in terms of the
presently preferred embodiments, it is to be understood that such
disclosure is not to be interpreted as limiting. Various alterations and
modifications will no doubt become apparent to those skilled in the art
to which the present invention pertains, after having read the above
disclosure. Accordingly, it is intended that the appended claims be
interpreted as covering all alterations and modifications as fall within
the true spirit and scope of the invention.